Miller, Stephen Andrew

2021-4-5, Valley, Benoît, Miller, Stephen Andrew

Switzerland initiated an energy transition plan for a massive development of renewable energy sources in response to climate change challenges and the decision to shut down nuclear power plants. Geothermal energy represents one component of this transition, with energy scenarios planning for more than 5% of the Swiss electricity demand produced from geothermal energy by 2050. Geothermal energy potentially provides base-load electricity supply, while also contributing to direct and indirect heat supply for replacing fossil fuels, and thus reducing greenhouse gas emissions. In response to this initiative, the Swiss Geological Survey (swisstopo) compiles information of the subsurface relevant for deep geothermal energy, including well data, seismic data interpretation of major stratigraphic horizons and faults, heat flux maps, thermal models of the underground, and geothermal potential studies. Access to this database provides opportunities for reviewing the geothermal potential of Switzerland using a quantitative play-fairway approach. In this contribution, we first review the available data sets and propose conceptual classifications of geological and structural settings favorable for deep-seated fluid circulation in Switzerland. We use the available data to determine best-estimate stress models, which are then used to compute slip and dilation tendency on the main faults identified in the database. We also combine all available information to provide quantitative mapping of the fairway score (favorability maps) for geothermal exploration. Model resolution does not yet capture local effects relevant for specific project development, but does identify general trends at the scale of Switzerland. Currently, this approach provides best estimate models for the currently available data, and will be refined and better-resolved with the acquisition and implementation of future data.

2001, Miller, Stephen Andrew

The strength of seismogenic faults is fundamental to earthquake mechanics and plate tectonics, affecting many subsidiary processes in the solid earth. The key to understanding fault strength is determining the pore pressures and hydraulic properties within the faults and surrounding crust. The debate has lasted over decades, with evidence provided for both strong fault and weak fault scenarios. A recently proposed hypothesis for quantifying the strength at which faults fail uses earthquake scaling arguments to show that earthquakes fail over a range of strengths in the upper 15-20 km, and at near-lithostatic pore pressure below this depth. This observation, if correct, has important implications for crustal hydraulics, plate tectonics, and earthquake hazard assessment. This paper summarizes the arguments for high pore pressure faulting, and explores its implications for earthquake stress drops, strength of the lithosphere, and earthquake scaling. The hope is to establish a general framework for quantifying the role of fluids in the earthquake process, and to demonstrate that high fluid pressure may dominate failure of the brittle crust.

2016-11-26, Schmitt, Nicole, Verbeken, B., Grassi, R., Miller, Stephen Andrew, Perrochet, Léa, Valley, Benoît, Mosar, Jon

2015-10-26, Schmitt, Nicole, Grassi, R., Miller, Stephen Andrew, Perrochet, L., Valley, Benoît, Mosar, Jon